1. Field of the Invention
The invention relates to a vane pump that supplies pressurized oil to, for example, a transmission or a power steering system of a vehicle.
2. Description of the Related Art
A vane pump described in, for example, Japanese Patent Application Publication No. 10-306783 (JP-A-10-306783) is used to supply pressurized oil to, for example, a transmission or a power steering system of a vehicle.
This vane pump includes a housing, a cam ring, and a rotor. The housing is fixed to a component to which hydraulic pressure is supplied (hereinafter, referred to as “hydraulic pressure supply destination component”), for example, a transmission. The cam ring is provided in the housing, and has an inner peripheral face that is in a noncircular shape in a cross section and that is used as a cam face. The rotor is provided on the inner side of the cam ring, and rotates about a rotating shaft. The housing is formed of a front housing, a rear housing and a side plate. In a housing recess of the front housing, the side plate and the cam ring are stacked in this order from the bottom side. The rear housing is fixed to the front housing so as to cover an opening of the housing recess. One of the side faces of each of the cam ring and the rotor contacts the side plate, and the other side face of each of the cam ring and the rotor contacts the rear housing. Multiple slits that extend in the radial direction are formed in the outer peripheral face of the rotor at regular intervals in the circumferential direction. Vanes are slidably fitted in the slits. When driving force is input in the rotating shaft, the rotor rotates while the ends of the vanes slide on the cam face. As the rotor rotates, the volume of each vane chamber formed between consecutive vanes changes. The change in the volume of each vane chamber causes pumping action. The pressurized oil is introduced into the vane chambers through an inlet formed in the side plate, and delivered to an outlet that is also formed in the side plate.
The vane pump uses the hydraulic pressure, which is generated by the vane pump itself, as urging force that urges the vanes in such a direction that the vanes project from the outer periphery of the rotor in order to move the vanes while the vanes slide on the cam face. More specifically, at a position that corresponds to the inner end portion of each slit, a vane back-pressure chamber is formed by the inner end portion, the side plate and the rear housing. The outlet is connected to the vane back-pressure chamber through a back-pressure introduction passage formed in the side plate. A portion of the pressurized oil delivered to the outlet is introduced into the vane back-pressure chamber, and the hydraulic pressure of the pressurized oil acts as the urging pressure that urges the vane in such a direction that the vane projects from the outer periphery of the rotor.
However, in this vane pump, the rotor and the side plate are arranged next to each other in the axial direction in the housing in order to form the back-pressure introduction passage through which the discharge pressure is introduced from the outlet to the vane back-pressure chamber. Therefore, the axial length of the vane pump is increased by an amount corresponding to the side plate. There is a demand to reduce the axial length of the vane pump in order to reduce the installation space for the vane pump. However, there is a limit to reduction in the axial length of the vane pump because the side plate is an indispensable component.